This present application relates generally to apparatus, methods and/or systems for improving the efficiency and/or operation of turbine engines, which, as used herein, is meant to include gas turbine engines, aircraft turbine engines, steam turbine engines, and other types of rotary engines. More specifically, but not by way of limitation, the present application relates to apparatus, methods and/or systems pertaining to turbine airfoil cooling orifices.
A gas turbine engine typically includes a compressor, a combustor, and a turbine. The compressor and turbine generally include rows of airfoils that are axially stacked in stages. Each stage includes a row of circumferentially-spaced stator blades, which are fixed, and a row of rotor blades, which rotate about a central axis or shaft. In operation, generally, the compressor rotor blades rotate about the shaft, and, acting in concert with the stator blades, compress a flow of air. The supply of compressed air then is used in the combustor to combust a supply of fuel. Then, the resulting flow of hot expanding gases from the combustion, i.e., the working fluid, is expanded through the turbine section of the engine. The flow of working fluid through the turbine induces the rotor blades to rotate. The rotor blades are connected to a central shaft such that the rotation of the rotor blades rotates the shaft.
In this manner, the energy contained in the fuel is converted into the mechanical energy of the rotating shaft, which, for example, may be used to rotate the rotor blades of the compressor, such that the supply of compressed air needed for combustion is produced, and the coils of a generator, such that electrical power is generated. During operation, because of the extreme temperatures of the hot-gas path, the velocity of the working fluid, and the rotational velocity of the engine, turbine airfoils, which, as described, generally include both the rotating rotor blades and the fixed, circumferentially-spaced stator blades, become highly stressed with extreme mechanical and thermal loads.
The ever-increasing demand for energy makes the objective of engineering more efficient turbine engines an ongoing and significant one. While several strategies for increasing the efficiency of turbine engines are known, it remains a challenging objective because these alternatives, which, for example, include increasing the size of the engine, increasing the temperatures through the hot-gas path, and increasing the rotational velocities of the rotor blades, generally place additional strain on parts, including additional strain on turbine airfoils, which, as stated, are already highly stressed. As a result, improved apparatus, methods and/or systems that reduce operational stresses and/or temperatures placed on turbine airfoils or allow the turbine airfoils to better withstand these stresses are in great demand.
As one of ordinary skill in the art will appreciate, one strategy for alleviating the distress of the airfoils is through cooling them such that the temperatures experienced by the airfoils are lower than that of the hot-gas path. Effective cooling, for example, may allow the airfoils to withstand higher firing temperatures, withstand greater mechanical stresses at high operating temperatures, and/or extend the part-life of the airfoil, all of which may allow the turbine engine to be more cost-effective and efficient in its operation. One way to cool airfoils during operation is through the use of internal cooling passageways or circuits. Generally, this involves passing a relatively cool supply of compressed air, which may be supplied by the compressor of the turbine engine, through internal cooling circuits within the airfoils. As the compressed air passes through the airfoil, it convectively cools the airfoil, which may allow the part to withstand firing temperatures that it otherwise could not.
In some instances, the supply of compressed air is released through small holes or apertures on the surface of the airfoils. Released in this manner, the air forms a thin layer or film of relatively cool air at the surface of the airfoil, which both cools and insulates the part from the higher temperatures that surround it. This type of cooling is commonly referred to as “film cooling.” Generally, to adequately cool the airfoil, numerous film cooling apertures, which generally are hollow passageways from interior cavities to the surface of the part, are necessary. However, as one of ordinary skill in the art will appreciate, per conventional methods, cooling apertures of this nature are somewhat time-consuming to manufacture. More significantly, once drilled, the cooling apertures become substantially impossible to modify. Additionally, given the geometry and nature of an airfoil, it is very difficult to fabricate complex cooling apertures, which may allow for better cooling properties. As a result, there is a need for improved apparatus, methods and/or systems relating to the more efficient and cost effective creation of turbine cooling apertures.